Perhaps the most successful construction for a conveyor belt capable of negotiating a right- or left-hand turn while remaining laterally flat comprises an assembly of pickets, or links, and rods, or belt members, that are uniquely conjoined. The pickets are nested and joined by inserting a straight rod, or belt member, through the trailing hole of the leading pickets, and the front end slots of the trailing pickets. Each end of the rod is provided with a head to retain the pickets on the respective connector rods. A longitudinal series of such pickets, each sequentially nested and operatively conjoined to the next successive picket by a connector rod comprises the desired conveyor belt of the type for which the subject invention is primarily intended. Further details of the aforesaid conveyor belt are disclosed in U.S. Pat. No. 3,348,659 and Re. Pat. No. 27,690 and are sold under the registered trademarks OMNI-GRID and OMNIFLEX.
Because of the capability of the aforesaid conveyor belts to negotiate turns, while remaining laterally flat, as well as to move in a straight line--i.e., a straightaway--they obviate the necessity for effecting transfers at the transition between a straightaway run and a turn. In addition, such a conveyor belt construction permits the conveyor to be employed in such a way as to effect the most efficient use of space. That is, the conveyor belt may be oriented in either an ascending or a descending spiral, or helix. The number of spiral tiers through which such a conveyor may pass is, as hereinafter more fully explained, limited only by the vertical "lead" of the helix when considered in conjunction with the height of the ceiling where the arrangement is located. For all practical purposes the minimum spiral lead available is equal to the height of whatever is to be supported on the conveyor plus the thickness of the conveyor belt, its supporting structure and the clearance desired between the successive passes of the conveyor.
To minimize tensile loading on the conveyor belt the spiral disposition of the conveyor belt continuously engages a cylindrical cage which is itself rotated to effect a simultaneous application of the driving force to the entire length of the conveyor which engages the cage. A plurality of such cages may be employed with the conveyor belt disposed in ascending and descending combinations to provide the length of conveyor necessary to accomplish the process effected thereon.
As is well known, the radius around which the aforedescribed flat belt conveyor can be flexed is determined by the geometry of the nested pickets, the degree to which they can telescope and the dimensions of the slots through which the connector rods are received in each picket. Manufacturers of the aforesaid conveyor belts have determined the optimum configuration for the pickets as well as the dimensions for the slots, and with those aspects of the pickets standardized the minimum turning radius of the belt is a function of the width of the conveyor belt itself. Current slot dimensions, and picket configurations, are such as to establish a nominal inside turning radius of 2.2 times the width of the conveyor belt. On that basis such a conveyor belt, when disposed in a spiral configuration about a cage, demands that the minimum outside diameter of the spiral be equal to 6.4 times the width of the belt.
As can be readily understood, the aforesaid relationship permits a most efficient use of precious floor space. That fact, taken in conjunction with the multitudinous tiers permitted by such an arrangement affords an idealized use of space.
A plurality of discrete objects can be conveyed along a straightaway or through turns on the aforedescribed conveyor belt in a virtually endless flow without jostling or undesirable localized accumulations. However, as desirable as a spiral arrangement may be for conveying discrete objects, it is seriously deficient when attempting to convey a continuous strip, or ribbon, of material having any appreciable width. For example, in the rubber industry continuous ribbons of material having appreciable width must be cooled and/or cured. The cooling and/or curing process may require that the ribbon of material move through an extended distance, which distance is a function of the rate at which the ribbon is being supplied and the length of time required to effect the desired result. To continue moving the ribbon in a straight line at the rate it is being fed, and for the time required, often requires an inordinate amount of space. To be able to accomplish the desired process during passage of the ribbon through one or more spiral arrangements of a conveyor belt would, therefore, be highly desirable except for the fact that a flat ribbon cannot negotiate a spiral path without deleterious results. That is, one side of the ribbon may be unduly subjected to compressive stresses and the other side may be unduly subjected to tensile stresses. In addition, it may even be virtually impossible to retain the ribbon on the conveyor belt itself.